1. Field of The Invention
This invention relates to a process for preparing silacyclohexane compounds which are useful as liquid crystal substance for liquid crystal display devices.
2. Description of the Prior Art
The liquid crystal display devices make use of optical anisotropy and dielectric anisotropy of liquid crystal substances. Depending on the mode of display, a variety of display systems are known including those of a twisted nematic type (TN type), a supertwisted nematic type (STN type), a super birefringence type (SBE type), a dynamic scattering type (DS type), a guest/host type, a type of deformation of aligned phase (DAP type), a polymer dispersion type (PD type), and an optical mode interference type (OMI type). The most popular display device is one which is based on the Schadt-Helfrich effect and has a twisted nematic structure.
Although the properties of the liquid substances used in these liquid crystal devices depend, more or less, on the type of display, it is commonly required that the liquid crystal substances have a wide range of liquid crystal working temperatures and that they are stable against moisture, air, light, heat, electric field and the like. Moreover, the liquid crystal substances should desirably be low in viscosity and should ensure a short address time, a low threshold voltage and a high contrast in cells.
As the liquid crystal display devices have wider utility in recent years, the characteristic properties required for liquid crystal materials become much severer. In addition, those characteristics which have never been required for conventional liquid crystal substances are now expected such as a lower drive voltage, a wider working temperature range which could satisfy on-vehicle needs and an improvement in low temperature performance.
Under these circumstances, we developed novel liquid crystal compounds which contain a silicon atom in the molecule so that the characteristic properties for use as a liquid crystal substance are improved, and proposed such liquid crystal compounds and preparation thereof in our earlier Japanese Patent Applications as will be set out hereinafter. As liquid crystals compounds, a trans form is useful. The liquid crystal compounds which we developed are obtained as a mixture of cis and trans forms. Although the mixture may be used in liquid crystal display devices, usual practice is to separate the trans form compound from the mixture.